<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<div id="app">

<input v-model="username">
{{username}}

</div>
<script src="js/vue.js"></script>
<script>
  //1.创建vue核心对象
  new Vue({
    el:"#app",
    data(){
      return{
        username:""
      }
    }


  })
</script>

</body>
</html>